Tissue David T, Barbour Margaret M, Hunt John E, Turnbull Matthew H, Griffin Kevin L, Walcroft Adrian S, Whitehead David
Department of Biology, Texas Tech University, Lubbock, TX 79409-3131, USA.
Plant Cell Environ. 2006 Apr;29(4):497-510. doi: 10.1111/j.1365-3040.2005.01427.x.
Seven methods, including measurements of photosynthesis (A) and stomatal conductance (g(s)), carbon isotope discrimination, ecosystem CO2 and water vapour exchange using eddy covariance and the use of a multilayer canopy model and ecosystem Keeling plots, were employed to derive estimates of intercellular CO2 concentration (Ci) across a range of spatial and temporal scales in a low productivity rain forest ecosystem dominated by the conifer Dacrydium cupressinum Lamb. in New Zealand. Estimates of shoot and canopy Ci across temporal scales ranging from minutes to years were remarkably similar (range of 274-294 micromol mol(-1)). The gradual increase in shoot Ci with depth in the canopy was more likely attributable to decreases in A resulting from lower irradiance (Q) than to increases in g, due to changes in air saturation deficit (D). The lack of marked vertical gradients in A and g(s) at saturating Q through the canopy and the low seasonal variability in environmental conditions contributed to the efficacy of scaling Ci. However, the canopy Ci estimate calculated from the carbon isotope composition of respired ecosystem CO2 (delta13CR; 236 micromol mol(-1)) was much lower than other estimates of canopy Ci. Partitioning delta13CR into four components (soil, roots, litter and foliage) indicated root respiration as the dominant (> 50%) contributor to delta13CR. Variable time lags and differences in isotopic composition during photosynthesis and respiration make the direct estimation of canopy Ci from delta 13CR problematic.
在新西兰以针叶树新西兰陆均松为主导的低生产力雨林生态系统中，采用了七种方法来估算细胞间二氧化碳浓度（Ci），这些方法包括光合作用（A）和气孔导度（g(s)）的测量、碳同位素判别、利用涡度协方差的生态系统二氧化碳和水汽交换以及多层冠层模型和生态系统基林曲线的应用，估算范围跨越一系列空间和时间尺度。从分钟到年的时间尺度上，茎和冠层Ci的估算值非常相似（范围为274 - 294微摩尔摩尔⁻¹）。冠层中茎Ci随深度的逐渐增加更可能归因于较低光照强度（Q）导致的A下降，而非空气饱和亏缺（D）变化引起的g增加。在饱和Q条件下，冠层中A和g(s)缺乏明显的垂直梯度以及环境条件的低季节性变化有助于Ci尺度转换的有效性。然而，根据呼吸的生态系统二氧化碳的碳同位素组成（δ¹³CR；236微摩尔摩尔⁻¹）计算出的冠层Ci估算值远低于其他冠层Ci估算值。将δ¹³CR分为四个组分（土壤、根系、凋落物和叶片）表明根系呼吸是δ¹³CR的主要贡献者（> 50%）。光合作用和呼吸过程中可变的时间滞后以及同位素组成的差异使得从δ¹³CR直接估算冠层Ci存在问题。
